create user 'test_user'@'localhost';
create role test_role1;
create role test_role2;
grant test_role1 to test_user@localhost;
grant test_role2 to test_user@localhost;
grant test_role2 to test_role1;
select user, host from mysql.user where user not like 'root';
user	host
test_role1	
test_role2	
test_user	localhost
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
	test_role1	test_role2	N
localhost	root	test_role1	Y
localhost	root	test_role2	Y
localhost	test_user	test_role1	N
localhost	test_user	test_role2	N
select user, host from mysql.db;
user	host
	%
	%
grant select on mysql.* to test_role2;
flush privileges;
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table 'roles_mapping'
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	NULL
set role test_role1;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	test_role1
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
	test_role1	test_role2	N
localhost	root	test_role1	Y
localhost	root	test_role2	Y
localhost	test_user	test_role1	N
localhost	test_user	test_role2	N
set role none;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	NULL
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table 'roles_mapping'
set role test_role2;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	test_role2
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
	test_role1	test_role2	N
localhost	root	test_role1	Y
localhost	root	test_role2	Y
localhost	test_user	test_role1	N
localhost	test_user	test_role2	N
drop user 'test_user'@'localhost';
revoke select on mysql.* from test_role2;
delete from mysql.user where user='test_role1';
delete from mysql.user where user='test_role2';
delete from mysql.roles_mapping where Role='test_role1';
delete from mysql.roles_mapping where Role='test_role2';
flush privileges;